1. Field of the Invention
The present invention relates to a heat treatment method and a heat treatment apparatus for emitting a light to a thin-plate-type precision electronic substrate (hereinafter simply referred to as a “substrate”) such as a semiconductor wafer or a glass substrate for a liquid crystal display device, to thereby heat the substrate.
2. Description of the Background Art
Conventionally, a lamp annealer including a halogen lamp has been generally used in a process of activating impurity (ion) of a semiconductor wafer after ion implantation. In such a lamp annealer, the semiconductor wafer is heated (annealed) to a temperature of, for example, approximately 1000 to 1100 degrees C., to thereby achieve an activation of the impurity of the semiconductor wafer. In this heat treatment apparatus, energy of a light emitted from the halogen lamp is utilized to raise the temperature of the semiconductor wafer at a rate of approximately several hundreds of degrees C. per second.
In recent years, a high integration of a semiconductor device is being advanced. As a gate length is accordingly shortened, a reduction in a junction depth is demanded. However, the fact has been revealed that even when the above-mentioned lamp annealer that raises the temperature of the semiconductor wafer at a rate of approximately several hundreds of degrees C. per second is used for activating the impurity of the semiconductor wafer, a phenomenon still occurs in which the impurity such as boron or phosphorus implanted in the semiconductor wafer is diffused deeply. Occurrence of such a phenomenon makes a junction depth deeper than required, which may undesirably obstruct the formation of a good device.
Accordingly, for example, U.S. Pat. Nos. 6,998,580 and 6,936,797 propose a technique in which a xenon flash lamp (hereinafter, the xenon flash lamp will be meant by the simple wording of “flash lamp”) is used to emit a flashing light to a surface of a semiconductor wafer so that the temperature of only the surface of the ion-implanted semiconductor wafer is raised to approximately 1100 degrees C. in an extremely short time period (equal to or shorter than a few milliseconds). A spectral distribution of the emission of the xenon flash lamp extends over an ultraviolet region through a near-infrared region, which has a wavelength shorter than that of a conventional halogen lamp and is substantially coincident with a fundamental absorption band of a silicon semiconductor wafer. Therefore, when a flashing light is emitted from the xenon flash lamp to the semiconductor wafer, the temperature of the semiconductor wafer can be quickly raised with a small amount of transmission light. The fact has also been revealed that an emission of the flashing light in an extremely short time period equal to or shorter than a few milliseconds enables the temperature of a semiconductor wafer to be raised selectively only in a portion near a surface thereof. Thus, if the temperature rise is caused in an extremely short time period by the xenon flash lamp, only an activation of impurity can be achieved without deep diffusion of the impurity.
Here, since an annealing process using the emission of the flashing light can raise the temperature of the surface of the semiconductor wafer up to a high temperature of 1100 degrees C. or higher in an extremely short time period, the process is effective in suppressing diffusion of implanted impurity and in activating the impurity, but is not suitable for recovery of crystal defects in silicon introduced during the implantation of the impurity. If a semiconductor device such as an FET (Field Effect Transistor) is prepared without a sufficient recovery of crystal defects, a problem occurs that a leakage current increases.